Part 1 Equivalent Resources of Canada, Mexico and Wright Et Al., 2010)

shale exploration Unconventional Methods For Unconventional Plays: Using Elemental Data To Understand Shale Resource Plays Ken Ratcliffe and Milly Wright, Chemostrat; Dave Spain, BP USA Part 1 equivalent resources of Canada, Mexico and Wright et al., 2010). Published accounts using hales are an important hydrocarbon the United States and it exceeds the estimated this approach are largely on fluvial successions, resource; yet understanding them as recoverable reserves of CSG in Australia. where stratigraphic correlation using traditional S reservoirs remains problematic. Their techniques are often problematic (e.g. Pearce fine-grained, organic-rich yet superficially Despite the activity and the large number of et al., 2005, Ratcliffe et al., 2006, Ratcliffe et homogenous character make the application well completions, the fine grained, macro-scale al., 2010, Wright et al., 2010 and Hildred et al., of traditional reservoir characterisation homogeneity of many formations currently 2011). Over the same decade, inorganic whole methods impractical or impossible. being exploited in North America negates some rock geochemical datasets have routinely been Increasingly, in the North American shale of the more traditional approaches to reservoir acquired from mudrocks, the data typically plays, inorganic geochemical data are being characterisation and stratigraphic correlation, being used to help elucidate paleoredox used as a one-stop method for understanding which has resulted in the search for new conditions during oceanic anoxic events (e.g. shale reservoirs. For decades, elemental data methodologies that enable better stratigraphic Tribovillard et al., 2006, Turgen and Brumsack, have been used to help solve stratigraphic understanding of shale reservoirs. Here, the 2006, Tribovillard et al., 2008, Negri et al., problems, i.e. definition of chemostratigraphic application and potential of one approach 2009, Jenkyns, 2010). Here, approaches of the frameworks. However, the same dataset is demonstrated, namely the application of chemostratigrapher and the oceanic anoxic acquired for chemostratigraphic studies can inorganic whole rock geochemical data (or event are combined and pragmatically applied be used to model shale mineralogy, model chemostratigraphy) to shale resource plays. to shale gas plays in North America. TOC levels, determine paleoredox conditions, identify zones of biogenic silica in shales and Inorganic whole rock geochemical data have While the applications presented here are largely provide information about transgressive – been used to define stratigraphic correlations tested on the Haynesville Formation and, to a lesser regressive cycles. in the petroleum industry for over a decade extent, the Eagle Ford and Muskwa formations, now (Ratcliffe et al., 2010 and references cited the approaches adopted herein would be equally The applications of elemental data to therein). The technique of chemostratigraphy applicable to any shale resource play. understanding shale plays fall into two natural relies upon recognising changes in element groupings. The first is the traditional use of concentrations through time and using those Methodology and dataset geochemical data to aid in understanding to model changes in geological features, such regional and reservoir-scale stratigraphy. This as paleoclimate (Pearce et al., 2005, Ratcliffe et The data for this article are largely from the application is discussed in this issue of PESA News al., 2010) and provenance (Ratcliffe et al., 2007, Haynesville Formation, with less extensive datasets Resources. The second main use geochemical data is in modeling applications, such as those listed above, and this will be discussed in the next issue of PESA News Resources. Introduction In the past decade, shale resource plays have risen to the forefront of hydrocarbon exploration, as shown by the numerous 'shale conferences' in the past two years alone (Critical Assessment of Shale Resource Plays, Hedberg Research Conference Dec 2010, Austin, Texas, World Shale Gas Conference & Exhibition, Nov 2010, Dallas Forth Worth, Texas, Nov 2011, Houston, Texas, Global Unconventional Gas Conference, June 2010, Amsterdam, Shale Gas World Europe, Dec 2010, Warsaw, Poland, Shale Gas Insight 2011, Nov 2011 Philadelphia, Pennsylvanian, Shale Gas Asia 2011, Feb, New Delhi, India to name but a few). Although the majority of active producing shale plays are in North America, the success there has led to increased interest in shale formations around the world, including in Australia, where according to a June 2011 report commissioned by the US Energy Information Agency, Australia has 396 Tcf of technically recoverable shale gas resources. This is equivalent to about 20% of the combined Fig. 1. Geographic location and ages of the shale reservoir plays referred to in the text. February/March 2012 | PESA News Resources | 89 shale exploration from the Muskwa Formation and the Eagle Ford Formation also being drawn upon (Figure 1). All TERREX GROUP of these formations are proven shale gas plays, with each being extensively drilled for exploration, appraisal and production. The Haynesville Formation is Terrex Seismic Terrex Contracting late Jurassic (Kimmeridgian) in 2D, 3D & 4D Seismic Data Acquisition Seismic Line Preparation & Restoration age. It is a locally calcareous and Australia’s most Australia’s Largest Onshore Fleet Minimal Environmental Impact organic rich (TOC values are technologically 2-6%) mudrock that occurs in northeast Texas and northwest Terrex Geophysical Terrex Spatial innovative and Louisiana (Figure 1). It was 2D, 3D & 4D Planning & Design GPS, GIS Surveying experienced deposited in an extensive intra shelf basin on the young, In-field Processing & QC Seismic, Gravity, Geodetic Surveys providers passive margin of the US Gulf Digital Terrain Modelling & Hi-Res LiDAR of seismic Coast during a period of arid climatic conditions. Basement Fig. 2. Geochemical characterisation of the Haynesville Formation as penetrated in Well Watson-4. Logs for a series of key exploration faulting and salt movement elemental ratios are plotted relative to depth in order to characterise broad scale “Chemostratigraphic Packages” (Plot services controlled the initial water depths, A) and finer scale geochemical units Plot B). All samples analysed here are from conventional core and all data were resulting in regions of the sea bottom acquired using ICP OES MS with a Li-metaborate fusion preparation. having restricted communication with the open ocean and therefore palynomorphs are often thermally degraded. • Package 3 (transitional between the recurrently experiencing anoxic bottom water Also, electric log correlations are hampered by Haynesville and Bossier formations) is conditions. The Eagle Ford Formation is a dark the variable controls on U, K and Th. In typical identified by generally lower Fe2O3/MgO grey calcareous, locally organic-rich mudstone fluvial and shallow oxic marine settings the K, Th, and Rb/K2O values compared to Package of Cenomanian – Turonian age (Figure 1). It and U are all largely controlled by the amount 2 and lower Th/U values compared to sub-crops in south Texas forming a narrow strip of clay versus sand, enabling lithostratigraphic Package 4.This interval also displays that is 150 miles long. Over this distance, the and sequence stratigraphic correlations to be elevated CaO/Al2O3 values relative to Eagle Ford Shale Formation varies in thickness made from the gamma logs. However, in the Packages 2 and 4. from approximately 75 ft to 300 ft. The Muskwa Haynesville Formation, U is associated with Formation is Frasnian (Devonian) in age and is TOC and minerals derived from authigenic • Package 2 (equivalent to the Haynesville located in northern Alberta, northeastern British enrichment in anoxic conditions, whereas Formation) is characterised by higher Colombia and in the southern portion of the K and Th are associated with the amount of Fe2O3/MgO values than underlying Northwest Territories, Canada (Figure 1). terrigenous-derived material. These associations packages and lower Th/U and MgO/ are discussed in greater detail in Part 2 of (CaO+MgO) values than the overlying All data for this article have been acquired using this article. Therefore, using gamma logs for Package 4. Inductively Coupled Plasma Optical Emission stratigraphic correlations in shale gas plays is (ICP-OES) and Mass Spectrometry (ICP-MS), enigmatic. Furthermore, the apparent macro- • Package 1 (transitional between the following a Li-metaborate fusion procedure scale homogeneity of the mud-rocks precludes Haynesville and Smackover formations) (Jarvis and Jarvis, 1995). These preparation and the recognition of sedimentary facies that can is characterised by CaO/Al2O3 values that analytical methods provide data for 10 major be used for stratigraphic correlations, particularly are intermediate between those of elements (SiO2, TiO2, Al2O3, Fe2O3, MgO, MnO, when only cuttings samples are available. Packages 0 and 2, and lower Fe2O3/MgO CaO, Na2O, K2O, P2O5), 25 trace elements (Ba, Be, values than overlying packages. Co, Cr, Cs, Cu, Ga, Hf, Mo, Nb, Ni, Pb, Rb, Sc, Sn, Chemostratigraphy has been used to Sr, Ta, Tl, Th, U, V, W, Y, Zn, and Zr) and 14 rare characterise and correlate the Haynesville • Package 0 (equivalent to the Smackover earth elements (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Formation, along with underlying and Formation) is identified by high CaO/Al2O3 Ho, Dy, Er, Tm, Yb, and Lu). overlying portions of the Smackover

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